Involvement Of P53 Research Articles

P21 resists ferroptosis in osteoarthritic chondrocytes by regulating GPX4 protein stability

Ferroptosis is involved in the pathogenesis of osteoarthritis (OA) while suppression of chondrocyte ferroptosis has a beneficial effect on OA. However, the molecular mechanism of ferroptosis in OA remains to be elucidated. P21, an indicator of aging, has been reported to inhibit ferroptosis, but the relationship between P21 and ferroptosis in OA remains unclear. Here, we aimed to investigate the expression and function of P21 in OA chondrocytes, and the involvement of P21 in the regulation of ferroptosis in chondrocytes. First, we demonstrated that high P21 expression was observed in the cartilage from OA patients and destabilized medial meniscus (DMM) mice, and in osteoarthritic chondrocytes induced by IL-1β, FAC and erastin. P21 knockdown exacerbated the reduction of Col2a1 and promoted the upregulation of MMP13 in osteoarthritic chondrocytes. Meanwhile, P21 knockdown exacerbated cartilage degradation in DMM-induced OA mouse models and decreased GPX4 expression in vivo. Furthermore, P21 knockdown sensitized chondrocytes to ferroptosis induced by erastin, which was closely associated with the accumulation of lipid peroxides. In mechanism, we demonstrated that P21 regulated the stability of GPX4 protein, and the regulation was independent of NRF2. Meanwhile, we found that P21 significantly affected the recruitment of GPX4 to linear ubiquitin chain assembly complex (LUBAC) and regulated the level of M1-linked ubiquitination of GPX4. Overall, our results suggest that P21 plays an essential anti-ferroptosis role in OA by regulating the stability of GPX4.

Emerging role of tumor suppressor p53 in acute and chronic kidney diseases.

p53 is a major regulator of cell cycle arrest, apoptosis, and senescence. While involvement of p53 in tumorigenesis is well established, recent studies implicate p53 in the initiation and progression of several renal diseases, which is the focus of this review. Ischemic-, aristolochic acid (AA) -, diabetic-, HIV-associated-, obstructive- and podocyte-induced nephropathies are accompanied by activation and/or elevated expression of p53. Studies utilizing chemical or renal-specific inhibition of p53 in mice confirm the pathogenic role of this transcription factor in acute kidney injury and chronic kidney disease. TGF-β1, NOX, ATM/ATR kinases, Cyclin G, HIPK, MDM2 and certain micro-RNAs are important determinants of renal p53 function in response to trauma. AA, cisplatin or TGF-β1-mediated ROS generation via NOXs promotes p53 phosphorylation and subsequent tubular dysfunction. p53-SMAD3 transcriptional cooperation downstream of TGF-β1 orchestrates induction of fibrotic factors, extracellular matrix accumulation and pathogenic renal cell communication. TGF-β1-induced micro-RNAs (such as mir-192) could facilitate p53 activation, leading to renal hypertrophy and matrix expansion in response to diabetic insults while AA-mediated mir-192 induction regulates p53 dependent epithelial G2/M arrest. The widespread involvement ofp53 in tubular maladaptive repair, interstitial fibrosis, and podocyte injury indicate that p53 clinical targeting may hold promise as a novel therapeutic strategy for halting progression of certain acute and chronic renal diseases, which affect hundreds of million people worldwide.

Harmine prevents 3-nitropropionic acid-induced neurotoxicity in rats via enhancing NRF2-mediated signaling: Involvement of p21 and AMPK

Oxidative stress induced neurotoxicity is increasingly perceived as an important neuropathologic mechanism underlying the motor and behavioral phenotypes associated with Huntington's disease (HD). Repeated exposure to 3-nitropropionic acid (3-NP) induces neurotoxic changes which closely simulate the neuropathological and behavioral characteristics of HD. This study aimed at evaluating the prophylactic effects of the dual-specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A) inhibitor “harmine” against 3-NP-indued neurotoxicity and HD-like symptoms. The potential prophylactic effect of harmine (10 mg/kg/day; intraperitoneal) was investigated on 3-NP-induced motor and cognitive HD-like deficits, nuclear factor erythroid 2 like 2 (NRF2), AMP kinase (AMPK) and p21 protein levels and the gene expression of haem oxygenase-1 (Ho-1), NAD(P)H: quinone oxidoreductase-1 (Nqo-1) and p62 in addition to redox imbalance and histological neurotoxic changes in the striatum, prefrontal cortex, and hippocampus of male Wistar rats. Harmine successfully increased the protein levels of NRF2, AMPK and p21 and the gene expression of Ho-1, Nqo-1 and p62, restored redox homeostasis, and reduced CASPASE-3 level. This was reflected in attenuation of 3-NP-induced neurodegenerative changes and improvement of rats' motor and cognitive performance. This study draws attention to the protective role of harmine against 3-NP-induced motor and cognitive dysfunction that could be mediated via enhancing NRF2-mediated signaling with subsequent amelioration of oxidative stress injury via NRF2 activators, p21 and AMPK, in the striatum, prefrontal cortex, and hippocampus which could offer a promising therapeutic tool to slow the progression of HD.

25I-NBOMe, a phenethylamine derivative, induces adverse cardiovascular effects in rodents: possible involvement of p21 (CDC42/RAC)-activated kinase 1

Abuse of new psychoactive substances is an emerging social problem. Several phenethylamines are internationally controlled substances as they are likely to be abused and have adverse effects. Phenethylamine analog 2-(4-iodo-2,5-dimethoxyphenyl)-N-(2-methoxybenzyl)ethanamine (25I-NBOMe) has been reported as one of the most commonly abused psychoactive substance. However, the cardiotoxicity of this compound has not been extensively evaluated. Thus, in this study, we investigated the adverse cardiovascular effects of 25I-NBOMe, related to p21 (CDC42/RAC)-activated kinase 1 (PAK1). The cardiotoxicity of 25I-NBOMe was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, live/dead cytotoxicity assay, PAK1/CDC42 kinase assay, and in vivo electrocardiography (ECG). Also, we analyzed the expression level of PAK1, which is known to play key roles in the cardiovascular system. In the MTT assay, cell viability of 25I-NBOMe-treated H9c2 cells or primary cardiomyocytes of ICR mice decreased in a concentration-dependent manner. Results from the in vitro cytotoxicity assay in cardiomyocytes showed that 25I-NBOMe decreased the viability of H9c2 rat cardiomyocytes, and TC50 of 25I-NBOMe was found to be 70.4 μM. We also observed that 25I-NBOMe reduced PAK1 activity in vitro. Surface ECG measurement revealed that intravenous injection of 25I-NBOMe (doses of 1.0 and 3.0 mg/kg, corresponding to serum concentrations of 18.1 and 28.6 ng/mL, respectively) prolonged the QTc interval in SD rats. Furthermore, treatment with 25I-NBOMe downregulated the expression of PAK1 in the hearts of SD rats and H9c2 cells. In summary, our findings indicate that PAK1-related adverse effects of 25I-NBOMe can cause toxicity to cardiomyocytes and induce an abnormal ECG pattern in animals.

Abstract 2307: The p53/p21 complex is a functional unit that regulates cancer cell invasion and apoptosis by targeting Bcl-2 family proteins

Abstract Although well known as a transcription factor, the p53 tumor suppressor also exists in the cytoplasm (including the mitochondria) of normal and cancer cells. Moreover, nuclear p53 is translocated to the mitochondria upon apoptotic stimulation of cells. The cytoplasmic/mitochondrial p53 can bind pro-survival Bcl-2 family proteins (e.g., Bcl-2, Bcl-XL, and Bcl-w), liberating Bax therefrom. Bax then exerts its pro-apoptotic or anti-invasive function depending on experimental conditions. Given the ability of p53 to interact with p21, we investigated the possible involvement of p21 in these functions. Here, we show that whereas p53 can bind to Bcl-w alone, it requires p21 to liberate Bax from Bcl-w and suppress/promote cell invasion/death, respectively. p21 consistently binds Bcl-w, forming a p53/p21/Bcl-w complex. Only this trifold complex, but not any of the pairings, facilitates the release of Bax from Bcl-w. Accordingly, a p53 derivative incapable of binding p21 fails to mediate radiotherapy-induced tumor retardation and cell death in mice. We further show that Bcl-2 and Bcl-XL also serves as a target of p53/p21 cooperative action. Overall, our findings indicate that the p53/p21 complex rather than p53 itself regulates cell invasion and death by targeting Bcl-2 proteins. We propose that the p53/p21 complex is a functional unit that acts on multiple types of cellular components, providing a new foundation for understanding the tumor-suppressing functions of p53 and p21. Citation Format: Eun Mi Kim, Hong-Duck Um. The p53/p21 complex is a functional unit that regulates cancer cell invasion and apoptosis by targeting Bcl-2 family proteins [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2307. doi:10.1158/1538-7445.AM2017-2307

The p53/p21 Complex Regulates Cancer Cell Invasion and Apoptosis by Targeting Bcl-2 Family Proteins.

The tumor suppressor p53 binds prosurvival Bcl-2 family proteins such as Bcl-w and Bcl-XL to liberate Bax, which in turn exerts proapoptotic or anti-invasive functions depending on stress context. On the basis of our previous finding that p53 interacts with p21, we investigated the possible involvement of p21 in these functions. Here, we report that although p53 can bind Bcl-w alone, it requires p21 to liberate Bax to suppress cell invasion and promote cell death. p21 bound Bcl-w, forming a p53/p21/Bcl-w complex in a manner that maintained all pairwise p53/p21, p21/Bcl-w, and p53/Bcl-w interactions. This allowed Bax liberation from the complex. Accordingly, a p53 derivative incapable of binding p21 failed to mediate radiotherapy-induced tumor cell death in mice. Bcl-XL also served as a target of the cooperative action of p53 and p21. Overall, our findings indicate that the p53/p21 complex rather than p53 itself regulates cell invasion and death by targeting Bcl-2 proteins. We propose that the p53/p21 complex is a functional unit that acts on multiple cell components, providing a new foundation for understanding the tumor-suppressing functions of p53 and p21. Cancer Res; 77(11); 3092-100. ©2017 AACR.

Zyflamend, a polyherbal mixture, down regulates class I and class II histone deacetylases and increases p21 levels in castrate-resistant prostate cancer cells

BackgroundZyflamend, a mixture containing extracts of ten herbs, has shown promise in a variety of preclinical cancer models, including prostate cancer. The current experiments were designed to investigate the effects of Zyflamend on the expression of class I and II histone deacetylases, a family of enzymes known to be over expressed in a variety of cancers.MethodsCWR22Rv1 cells, a castrate-resistant prostate cancer cell line, were treated with Zyflamend and the expression of class I and II histone deacetylases, along with their downstream target the tumor suppressor gene p21, was investigated. Involvement of p21 was confirmed with siRNA knockdown and over expression experiments.ResultsZyflamend down-regulated the expression of all class I and II histone deacetylases where Chinese goldthread and baikal skullcap (two of its components) appear to be primarily responsible for these results. In addition, Zyflamend up regulated the histone acetyl transferase complex CBP/p300, potentially contributing to the increase in histone 3 acetylation. Expression of the tumor suppressor gene p21, a known downstream target of histone deacetylases and CBP/p300, was increased by Zyflamend treatment and the effect on p21 was, in part, mediated through Erk1/2. Knockdown of p21 with siRNA technology attenuated Zyflamend-induced growth inhibition. Over expression of p21 inhibited cell growth and concomitant treatment with Zyflamend enhanced this effect.ConclusionsOur results suggest that the extracts of this polyherbal combination increase histone 3 acetylation, inhibit the expression of class I and class II histone deacetylases, increase the activation of CBP/p300 and inhibit cell proliferation, in part, by up regulating p21 expression.

Anti-Tumor Effects of Mfn2 in Gastric Cancer

Mitofusin-2 (Mfn2) is a mitochondrial outer membrane protein involved in mitochondrial fusion. Its mutation can cause Charcot-Marie-Tooth disease. Recent studies of Mfn2 in cancer research have not included gastric cancer. We confirmed that Mfn2 expression was lower in tumor tissue than in normal gastric mucosal tissue and that it was negatively correlated with tumor size, indicating an anti-tumor role for Mfn2. In vitro experiments showed that Mfn2 overexpression suppressed gastric cancer cell proliferation and colony formation, weakened the invasion and migratory ability of cancer cells by downregulating MMP-2 and MMP-9, halted the cell cycle and induced apoptosis. Western blotting indicated the likely involvement of P21 and PI3K/Akt signaling. Therefore, Mfn2 is a potential anti-tumor gene and a potential therapeutic target for treating gastric cancer. The progress of gastric cancer may be delayed by controlling Mfn2 expression.

Improved sorafenib activity on hepatocellular carcinoma in Notch3 silenced in vivo and in vitro models.

3061 Background: Sorafenib is the only approved drug for the treatment of the advanced stage of HCC. Although its efficacy has been proven with randomized clinical trials, the clinical benefit seen in overall survival for advanced HCC patients treated with sorafenib could be improved. New molecules or combination of novel targeted agents to improve sorafenib efficacy for advanced stage HCC patients are needed. Notch genes are a family of receptors involved in many cell fate regulations, their expression has been found altered in many tumors, including HCC. The aim of this study was to study the combination of sorafenib and Notch3 signaling inhibition to improve sorafenib’s therapeutic effect. Methods: HepG2 and Huh7 cellular models were used for Notch3 stable silencing by retroviral introduction of specific interfering RNAs Xenograft models in both Notch3 stable shRNA cell lines have been developed using NOD/SCID mice. Animals bearing tumors were treated with 60 mg/kg of sorafenib for 21 consecutive days. Notch3, p21 and pGSK3βSer9 protein expression were also analyzed in 20 human HCCs. Results: Notch3 silencing (shN3) in HuH7 and HepG2 cell lines treated with sorafenib showed an increase in cell death (3.8 to 5 fold increase) when shN3 cell lines were compared with their relative controls (GL2). A difference in tumor growth was observed between GL2 negative control vs shN3 xenografts in both HepG2 and Huh7 after 21 days of sorafenib treatment. Two tailed student’s t test (shN3 vs GL2) P=0,04 and P=0,01 for Huh7 and HepG2 respectively. Molecular investigations have shown the involvement of p21 and GSK3β in the enhanced response to sorafenib in Notch 3 silenced models. A significant inverse correlation between Notch3 and pGSK3βSer9 proteins accumulation (Spearman ρ= -0.666) (p < 0.01) and a direct correlation between Notch3 and p21 proteins expression (Spearman ρ= 0.681) (p < 0.01) was found in HCC samples obtained from patients. Conclusion: Our preclincal findings outline the effect of combined Notch3 inhibition and sorafenib. The molecular mechanisms responsible for sorafenib induced cell death associated with Notch3 silencing relays on inhibition of p21/CDKN1A and GSK3βSer9. This study is supported by a grant from Bayer Healthcare, Italy.

Abstract 836: Rexinoids induce cellular senescence in ER-negative breast cancer cells and in MMTV-Neu mammary tumors

Abstract Retinoids and recently rexinoids have been extensively studied as potential cancer preventive agents. Their effects both in vitro and in vivo have been associated with inhibition of cell proliferation via cell cycle regulatory genes/proteins. In previous studies we have shown that retinoids (atRA, 9cRA), in addition to inhibition of cell proliferation, can also induce cellular senescence (CS) in breast cancer cell lines and in an MNU-model of mammary carcinogenesis in rats. We also found that atRA is more efficacious in inducing CS in ER+ than in ER− breast cancer cell lines. Here we examined the role of rexinoids (LGD1069) in inducing CS in ER− breast cancer cell lines and in ER− tumors of the MMTV-Neu model of mammary carcinogenesis in mice. CS was determined by SA-β-Gal staining, colony formation assay, heterochromatin condensation and histone H2AX expression. Cells grown on cover slips were treated for 6 days with 1.0 or 5.0 µM of LGD1069 and senescent cells identified. We found that LGD1069 at 1.0 µM is more efficacious in inducing CS in ER+ MCF-7 and T47D cells, 56% and 42% respectively vs. 14% and 9% in control cells. Normal MCF10A, premalignant MCF10AT, and malignant MDA-MB-231 and MDA-MB-468 cells, which are ER−, required 5.0 µM of LGD1069 to increase CS from 3.0, 6,0, 4.0 and 10.0% in control to 14, 24, 26 and 33% in treated cells. For in vivo studies, MMTV-Neu mice with palpable mammary tumors were treated for 4 weeks with 80 or 40 mg/kg body weight LGD1069, given by gavage. Proliferating cells (BrdU-labeled) in mammary tumors decreased from 9.6±2.3% in control animals (No=13) to 7.4±3.0% (p<0.01) (No=10) and to 5.6±2.5% (p<0.001) (No=12) in high and low dose treated animals, respectively. Senescent cells, as detected by SA-β-Gal staining, were rare in control tumors (0.92±0.23%) and significantly increased in LGD1069, 80 mg/kg treated animals (6.8±4.0%) (p<0.001). LGD1069 was unable to affect apoptosis. Our mechanistic studies suggest involvement of p21, RXRα and RARβ in mediating LGD1069-induced CS in ER− breast cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 836. doi:10.1158/1538-7445.AM2011-836

Matrine inhibits vascular smooth muscle cell proliferation by modulating the expression of cell cycle regulatory genes

To investigate the effect of matrine on proliferation of vascular smooth muscle cells (VSMCs) and elucidate the underlying mechanisms. Rat aortic VSMCs were cultured in medium supplemented with 10% fetal bovine serum and treated with various concentrations (0, 5, 10, 15, and 20 mg/L) of matrine for 72 h. VSMCs proliferation and cell cycle profiling were assessed using a methylene blue incorporation assay and flow cytometry, respectively. The underlying protein signaling mechanisms were determined using Western blot analysis of the expression levels of cell cycle regulatory genes, including p53, p21, p27, cyclin D1, cyclin E, cyclin-dependent kinase 2 and 4 (cdk2, cdk4), and phosphorylated Rb. The involvement of p21 and p27 pathways was further determined using small interfering RNA (siRNA) knockdown. Matrine inhibited VSMC proliferation in a dose-dependent manner by promoting G(1) arrest. The G(1) arrest was accompanied by up-regulation of p53 and p21 protein levels, and down-regulation of cyclin D1/cdk4, cyclin E/cdk2 and phosphorylated Rb protein levels. Matrine did not affect p27 expression. Furthermore, the anti-proliferative effect of matrine was abolished by silencing of p21, but not by silencing of p27. Our data indicate that matrine has an inhibitory effect on VSMC proliferation via up-regulation of the p53/p21 signaling pathway and modulation of other cell cycle regulatory genes.

Molecular targets of apigenin in colorectal cancer cells: Involvement of p21, NAG-1 and p53

Persuasive epidemiological and experimental evidence suggests that dietary flavonoids have anti-cancer activity. Since conventional therapeutic and surgical approaches have not been able to fully control the incidence and outcome of most cancer types, including colorectal neoplasia, there is an urgent need to develop alternative approaches for the management of cancer. We sought to develop the best flavonoids for the inhibition of cell growth, and apigenin (flavone) proved to be the most promising compound in colorectal cancer cell growth arrest. Subsequently, we found that pro-apoptotic proteins (NAG-1 and p53) and cell cycle inhibitor (p21) were induced in the presence of apigenin, and kinase pathways, including PKCδ and ataxia telangiectasia mutated (ATM), play an important role in activating these proteins. The data generated by in vitro experiments were confirmed in an animal study using APC MIN+ mice. Apigenin is able to reduce polyp numbers, accompanied by increasing p53 activation through phosphorylation in animal models. Our data suggest apparent beneficial effects of apigenin on colon cancer.

Involvement of Cell Cycle and Apoptosis-Related Protein p21 in Control of Secretory Activity of Porcine Ovarian Cells

Protein p21, member of the Cip/Kip family of cyclin kinase inhibitors, is a physiological regulator of cell cycle, differentiation and apoptosis in various cell types. Its role in regulation of secretory activity of both non-ovarian and ovarian tissues is unknown. The aim of our in-vitro experiments was to examine possible involvement of p21 in regulation of porcine ovarian granulosa cells secretory activity. Monolayer of primary granulosa cells was transfected with plasmid vector encoding human p21 cDNA, and cultured with or without addition of follicle-stimulating hormone (FSH) or insulin-like growth factor I (IGF-I) (both at 0, 1, 10 or 100 ng/ml). Release of IGF-I, progesterone (P4), oxytocin (OT), prostaglandins E2 (PGE2) and F2? (PGF2?) was assayed by using RIA. We observed, that (1) p21 promoted the release of P4, OT, PGE2 and had no impact on IGF-I and PGF2? output, (2) FSH stimulated the release of IGF-I and P4, (3) IGF-I enhanced the release of OT, P4 and PGE2 , but it inhibited the release of PGF2?, (4) overexpression of 21 was able to modify the effects of IGF-I, but not of FSH. Our observations (1) demonstrate for a first time the involvement of p21 in regulation of hormones release P4, OT and PGE2 by ovarian granulosa cells, (2) confirm the regulation of porcine ovarian hormone release by FSH and IGF-I and (3) suggest, that p21 is not a mediator of FSH action on porcine ovarian P4 and IGF-I; involvement of p21 in mediating IGF-I action on some porcine ovarian hormones is not to be excluded, but it requires further confirmation.

MiR-24 Tumor Suppressor Activity Is Regulated Independent of p53 and through a Target Site Polymorphism

MicroRNAs (miRNAs) are predicted to regulate approximately 30% of all human genes; however, only a few miRNAs have been assigned their targets and specific functions. Here we demonstrate that miR-24, a ubiquitously expressed miRNA, has an anti-proliferative effect independent of p53 function. Cell lines with differential p53 status were used as a model to study the effects of miR-24 on cell proliferation, cell cycle control, gene regulation and cellular transformation. Overexpression of miR-24 in six different cell lines, independent of p53 function, inhibited cell proliferation and resulted in G2/S cell cycle arrest. MiR-24 over expression in cells with wt-p53 upregulated TP53 and p21 protein; however, in p53-null cells miR-24 still induced cell cycle arrest without the involvement of p21. We show that miR-24 regulates p53-independent cellular proliferation by regulating an S-phase enzyme, dihydrofolate reductase (DHFR) a target of the chemotherapeutic drug methotrexate (MTX). Of interest, we found that a miR-24 target site polymorphism in DHFR 3′ UTR that results in loss of miR-24-function and high DHFR levels in the cell imparts a growth advantage to immortalized cells and induces neoplastic transformation. Of clinical significance, we found that miR-24 is deregulated in human colorectal cancer tumors and a subset of tumors has reduced levels of miR-24. A novel function for miR-24 as a p53-independent cell cycle inhibitory miRNA is proposed.

Involvement of p21 and FasL in Induction of Cell Cycle Arrest and Apoptosis by Neochamaejasmin A in Human Prostate LNCaP Cancer Cells

Neochamaejasmin A ( 1), a biflavonoid isolated from the roots of a traditional Chinese medicine, Stellera chamaejasme L., was shown to inhibit cellular (3)H-thymidine incorporation (IC 50 12.5 microg/mL) and subsequent proliferation of human prostate cancer LNCaP cells. Treatment of LNCaP cells with low doses of 1 (< or =6.25 microg/mL) suppressed DNA-binding activities of the transcription factors NFkappaB and AP-1 to the promoter of cyclin D and also inhibited expression of the cell cycle regulatory proteins cyclin D, proliferating cell nuclear antigen, and nucleolin, thus arresting cells in G 1 phase of the cell cycle. A lengthy exposure with higher doses of 1 (> or =12.5 microg/mL) revealed the production of reactive oxygen species, dissipation of the mitochondrial membrane potential, up-regulation of cyclin-dependent kinase inhibitor p21, and induction of cell apoptosis. An aggregation of Fas-procaspase 8-procaspase 3 and p21-procaspase 3 proteins by coimmunoprecipitation, immunoblotting analysis, and MALDI-mass spectrometry indicated the involvement of Fas and p21 in 1-mediated cytotoxicity, and pretreatment of cells with antisense FasL oligonucleotides partially abolished apoptosis. Thus, 1 blocked cell cycle progression at the G 1 phase by activating the p21 protein and ultimately promoting the Fas-caspase 8-caspase 3 apoptotic machinery.

Genetic dissection of the role of p21Cip1/Waf1 in p53-mediated tumour suppression

Protein p21Cip1/Waf1 is transcriptionally activated by the tumour suppressor p53 and previous studies have shown that p21 plays a role in tumour suppression. However, the involvement of p21 in p53-mediated tumour suppression remains to be directly demonstrated in vivo. Tumour suppression mediated by p53 can be measured by comparing tumour susceptibility in animals carrying two (wild-type mice) or three (super-p53 mice) copies of the p53 gene. We have taken advantage of this genetically defined system to measure p53-mediated cell-cycle arrest, apoptosis and tumorigenesis, in a p21 wild-type and in a p21-null context. The absence of p21 significantly impaired the enhanced p53-mediated cell-cycle arrest characteristic of super-p53 cells, but did not affect the enhanced apoptosis. Importantly, in an experimental model of fibrosarcoma induction, the absence of p21 significantly decreased the tumour suppression benefit of super-p53 mice. We conclude that cell-cycle arrest through p21 plays a significant role in mediating p53-dependent cancer protection.

Suppression of chondrosarcoma cells by 15-deoxy-Δ 12,14-prostaglandin J 2 is associated with altered expression of Bax/Bcl-xL and p21

We previously reported that 15-deoxy-Δ 12,14-prostaglandin J 2 (15d-PGJ 2), the most potent agonist for peroxisome proliferator-activated receptor γ (PPARγ), induces apoptosis of human chondrosarcoma cell line OUMS-27. The current study aimed to explore the mechanism of 15d-PGJ 2-induced apoptosis and inhibition of cell proliferation in OUMS-27 cells. The preliminary results of cDNA microarray analysis showed the down-regulation of anti-apoptotic Bcl-xL and up-regulation of pro-apoptotic Bax in the process of 15d-PGJ 2-induced apoptosis. These changes were further confirmed at mRNA and protein levels by RT-PCR and Western blot analysis, respectively. Among cyclin-dependent kinase inhibitors, p21 was induced and up-regulated by 15d-PGJ 2, but p16 and p27 were not changed, suggesting that the involvement of p21 in inhibition of cell proliferation. Activation of caspase-3 by 15d-PGJ 2 was partly, but not completely, blocked by PPARγ antagonist (GW9662) suggesting the 15d-PGJ 2 exerted its effect by PPARγ-dependent and -independent pathways. Interestingly, immunohistochemical study on human chondrosarcoma samples revealed that Bcl-xL is frequently expressed by tumor cells. The results of the current study suggest that the potential ability of 15d-PGJ 2 in regulation of cell cycle and inhibition of Bcl-xL expression might be beneficial in the development of novel pharmacological agents for chondrosarcoma.

Chromosome 13q12 encoded Rho GTPase activating protein suppresses growth of breast carcinoma cells, and yeast two-hybrid screen shows its interaction with several proteins

We have characterized the cDNA for a Rho GTPase activating protein (GAP) mapping to chromosome 13q12. The cDNA was characterized by determining the complete sequence of a 4.8 kb cDNA clone that represents the 5 ′ untranslated region (UTR), the translated region, and the 3 ′ UTR. The protein has a sterile α-motif (SAM), a distinct GAP domain, and a conserved START (StAR related lipid transfer) domain. The cDNA has 5 instability motifs (ATTTA) in the 3 ′ UTR and one motif in the translated region between GAP and START domains. The RhoGAP transcript is truncated in some breast carcinoma cell lines and it has low expression in other breast cancer cell lines as compared to a normal breast cell line. We have previously observed the absence of RhoGAP transcript in a breast tumor specimen. A GST-fusion of the RhoGAP was tested for its specificity on RhoA, Cdc42, and Rac1. The protein was most active for RhoA. Transfection of RhoGAP into MCF7 cells significantly inhibited cell growth. The introduction of the RhoGAP construct into MDAMB231 cells that had previously been transfected with a p21 construct did not affect cell proliferation, indicating the involvement of p21 in Rho-mediated proliferation of cancer cells. NIH3T3 cells overexpressing RhoGAP showed considerable inhibition of stress fiber formation. Several cDNAs were identified as RhoGAP interactors by using the yeast two-hybrid assay system. These cDNAs correspond to SWI/SNF, α-tubulin, HMG CoA reductase, and TAX1 binding protein (TAX1BP1). The interaction with HMG CoA reductase may partially explain the growth inhibition of breast carcinoma cells by statin class of cholesterol lowering drugs. The biological significance of the interacting proteins is discussed in the context of their involvement in tumorigenesis. Our results indicate that loss of RhoGAP or its altered activity suppresses the growth of breast tumor cells. The presence of various motifs in RhoGAP and its interaction with several other proteins suggest that the protein may regulate Rho signaling in multiple ways and possibly function in a Rho-independent manner.

High expression of p21WAF1/CIP1 is correlated with human hepatocellular carcinoma in patients with hepatitis C virus–associated chronic liver diseases

p21WAF1/CIP1 (p21) protein is a universal inhibitor of cyclin-dependent kinases and is regulated transcriptionally by p53, which is activated by DNA stress. Hepatocytes in chronic hepatitis receive several DNA stresses by lymphocytes and Kupffer cells. Therefore, we analyzed p21 expression of hepatocytes in hepatitis C virus (HCV)-associated chronic liver diseases and investigated the possible involvement of p21 in hepatocarcinogenesis. We examined p21 expression in 35 cases of HCV-associated chronic hepatitis and 25 cases of HCV-associated liver cirrhosis by immunohistochemical analysis. The p21 labeling index (LI) was calculated as the ratio of positive cells to total cells. p21-positive hepatocytes were more numerous in areas of intense inflammation and spotty necrosis and areas close to fibrosis, and were increased according to the degrees of grading and staging. The p21 LI with liver cirrhosis was significantly higher than that with chronic hepatitis (14.4 ± 5.9 versus 11.1 ± 4.2, P = 0.014). The cumulative incidence of hepatocellular carcinoma (HCC) was significantly higher in the p21 LI ≥14% group than in the p21 LI <14% group (P = 0.0079). Multivariate analysis demonstrated that p21 expression can be recognized as an independent significant factor for HCC development (relative risk 5.00, P = 0.039). p21 LI decreased significantly after interferon therapy. These results suggested that p21 is up-regulated by the stress of inflammation and fibrosis in HCV-associated chronic liver diseases and that high p21 expression might be related to hepatocarcinogenesis in cirrhotic patients. HUM PATHOL 33:429-434. Copyright 2002, Elsevier Science (USA). All rights reserved.

Involvement of p21(WAF1/Cip1), p27(Kip1), and p18(INK4c) in troglitazone-induced cell-cycle arrest in human hepatoma cell lines.

Peroxisome proliferator-activated receptor gamma (PPARgamma) regulates cell growth and differentiation. Recent evidence has suggested that PPARgamma ligands had anti-tumor effects through inhibiting cell growth and inducing cell differentiation in several types of malignant neoplasm. In the present study, we investigated: 1) the expression of PPARgamma in both human hepatoma cell lines and 5 resected human hepatocellular carcinoma (HCC) tissues; 2) the growth-inhibitory effect of troglitazone, a PPARgamma ligand, on those hepatoma cells; and 3) the molecular mechanisms of troglitazone-induced cell-cycle arrest. Five hepatoma cell lines, HLF, HuH-7, HAK-1A, HAK-1B, and HAK-5, were used. The mRNA expression levels of PPARgamma, p21(WAF1/Cip1), and p27(Kip1) were determined by real-time quantitative reverse transcription-polymerase chain reaction. The expression of cell cycle-regulating proteins, such as p21, p27, p18(INK4c), cyclin E, and pRb, was examined using Western blotting. PPARgamma was constitutively expressed in all the cell lines and the HCC tissues used in this study. A cytostatic effect of troglitazone was found in those cell lines, and this inhibition of cell growth was dosage-dependent. G0/G1 arrest was apparently demonstrated in flow cytometric analysis in HLF, HAK-1A, HAK-1B, and HAK-5, all of which showed an increased expression of p21 protein. However, HuH-7, lacking p21 protein expression, did not demonstrate clear arrest in the cell-cycle analysis. HLF, which was deficient in the protein product of the retinoblastoma tumor-suppressor gene (pRb), responded most profoundly to troglitazone, showing an increased expression in not only p21, but also in p27 and in p18. These findings suggested that p21, p27, and p18 might be involved in troglitazone-induced cell-cycle arrest in human hepatoma cells.